AncestryDNA, How to Find Your Shared DNA in Centimorgans

Do you know how to find the length of shared DNA with an AncestryDNA match in centimorgans (cMs)? If not, you are not alone. This is one of the most critical measures of a DNA relationship, yet Ancestry hides it away so that a user probably has to stumble across it. Why?! This week three of the DNA tests I bought for relatives over the holidays finished processing, yay. While on the phone with a relative who is a proficient genealogy researcher to discuss the results, she went straight to GEDmatch because she didn’t know AncestryDNA even showed the centimorgan match length. Until AncestryDNA changes their format, which they really should do, here is how to find your match length in centimorgans.

Start on your AncestryDNA page at http://www.ancestry.com/dna. (If you have access to multiple DNA tests, choose the tester you care about.) Select the green button “VIEW ALL DNA MATCHES.” The list of your matches pops up. Select the blue, underlined name of the match you are curious about. Up will pop a page about that individual. About four lines down from the top is the “Predicted Relationship” section. In that section is a little circled letter “i.” Select the letter “i” to see something like this:

Amount of Shared DNA

281 centimorgans shared across

12 DNA segments

What does this mean?

The number where I show 281 in the example is the one you care about. (The number of segments is less important; what would be more relevant is the longest segment length, which AncestryDNA doesn’t give us yet.) So perfect, we found our number.

Why is the centimorgans relevant? I will start with a reference to the ISOGG relationship chart at isogg.org/wiki/Autosomal_DNA_statistics that I wrote about here. If you are using DNA to search for unknown biological relatives like I am, the centimorgan match length, or “centimorgan score” some genealogists say, measures how much DNA two people share (in significant segment lengths over certain genome locations). The relationship chart can show you based on the centimorgan score what kinds of relationships you could have, and which ones are more likely. Vital for finding out how we could fit into the family.

So spread the word about finding and using the centimorgan score, so that others can make better use of their DNA results, and happy researching!